This application claims priority to United Kingdom (GB) Patent Application No. 0110456.1 filed on Apr. 28, 2001.
The present invention relates to a latch assembly. More particularly, the present invention relates to a latch assembly having an actuator with two output modes.
The present invention is particularly, although not exclusively, applicable to latches used on vehicle doors such as car passenger doors, tailgate doors or car trunk doors.
Vehicle door latches are known which are released using a power actuator.
From the point of the view of vehicle users, it is desirable that the unlatching of a vehicle door is achieved rapidly so that the user is not required to wait before they may enter the vehicle.
When the door is latched, the seals around the door exert an outward force tending to open the door that is reacted at the interface between the striker and latch bolt. This is commonly known as the xe2x80x98seal forcexe2x80x99. The configuration of conventional latch assemblies is such that an increased seal force in turn requires an increased unlatching force to be applied to unlatch the latch bolt. Thus, when the seal force is relatively low, a drive means with a relatively low power output is capable of rapidly unlatching the latch bolt to permit vehicle entry.
However, if the seal force is increased due to, for example, the buckling of the door in an impact, an attempt by the drive to rapidly unlatch the door is liable to cause the drive to stall and the door thus to remain latched. In order to overcome this problem, is has hitherto been necessary to provide a more powerful drive, which inevitably increases the cost of a latch assembly, or to slow the rate of unlatching so that a less powerful drive may provide an increased unlatching force that will overcome the higher seal force and thus permit unlatching to occur.
The present invention seeks to provide a latch arrangement having a relatively low power drive that can be rapidly unlatch the door under normal conditions, and yet provide high unlatching forces in high seal force conditions.
Accordingly, one aspect of the present invention provides a latch assembly for releasably securing a door in a closed position, the assembly comprising an actuator with an actuator output, the actuator having a first relatively fast acting low force output mode and a second relatively slow acting high force output mode, the actuator output being interconnected with a latch bolt of the assembly such that the latch bolt may be relatively rapidly released by the actuator operating in its first output mode when the load required to unlatch the latch bolt is relatively low, but relatively slowly unlatched by the second output mode when the load required to unlatch the latch bolt is relatively high.